The G2 system works great. I am about to paint the Calipers on my X5. They can do a color match for $99.00 or you can get the 11 standard colors for $37.50 on ebay for the G2. You mix it and have about 30-40 minutes to paint them. So prep first and get ready. Use a brush and a steady hand and have at it.
I have an ALPINE white X5 and I thought about just the standard white but I will probably paint them silver(like oem) or black. Both will have gloss from the G2. I like RED but the calipers on the X5 are not that big compared to the M5. I might do the M5 RED since it is Alpine White as well.
Can't go wrong with Silver or Black. Some people will try to give you a hard time about RED/YELLOW but I wouldn't pay attention to them
So what you want. It's your money, your car and your time.